Browsing by Author "Raeisi, Sajjad"

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    Design of a Hybrid Honeycomb Unit Cell with Enhanced In-Plane Mechanical Properties
    (SAE, 2019-04) Raeisi, Sajjad; Tapkir, Prasad; Ansari, Farha; Tovar, Andres; Mechanical and Energy Engineering, School of Engineering and Technology
    Sandwich structures with honeycomb core are widely used in the lightweight design and impact energy absorption applications in automotive, sporting, and aerospace industries. Recently, the auxetic honeycombs with negative Poisson's ratio attract substantial attention for different engineering products. In this study, we implement Additive Manufacturing technology, experimental testing, and Finite Element Analysis (FEA) to design and investigate the mechanical behavior of a novel unit cell for sandwich structure core. The new core model contains the conventional and auxetic honeycomb cells beside each other to create a Hybrid Honeycomb (HHC) for the sandwich structure. The different designs of unit cells with the same volume fraction of 15% are 3D-printed using Fused Deposition Modeling technique, and the comparative study on the mechanical behavior of conventional honeycomb, auxetic honeycomb, and HHC structures is conducted. The quasi-static uniaxial compression tests are performed on the printed samples to investigate the mechanical behavior of the printed structures. The deformation and failure modes of the different designs are studied at the cell level utilizing FEA of the compression test and experimental observation. The compressive strength of the different design is measured using three experimental tests. The new HHC unit cell design shows significantly higher mechanical properties than the auxetic and the conventional designs. Modifying the design variables of hybrid cellular core structure allows us to tailor the mechanical properties and deformation pattern in macro level to achieve the desired mechanical properties in sandwich structures.
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    The Effect of the Cell Shape on Compressive Mechanical Behavior of 3D Printed Extruded Cross-sections
    (2018) Raeisi, Sajjad; Tovar, Andres; Mechanical Engineering, School of Engineering and Technology
    Additive manufacturing has been a promising technique for producing sophisticated porous structures. The pore's architecture and infill density percentage can be easily controlled through additive manufacturing methods. This paper reports on development of sandwich-shape extruded cross sections with various architecture. These lightweight structures were prepared by employing additive manufacturing technology. In this study, three types of cross-sections with the same 2-D porosity were generated using particular techniques. a) The regular cross section of hexagonal honeycomb, b) The heterogeneous pore distribution of closed cell aluminum foam cross section obtained from image processing and c) linearly patterned topology optimized 2-D unit cell under compressive loading condition. The optimized unit cell morphology is obtained by using popular two-dimensional topology optimization code know as 99-line code, and by having the same volume fraction as the heterogeneous foam. The upper edge of the unit cell was under distributed uniform loading and the lower edge was fixed. All the cross sections have the same cavity to wall area ratio on their 2-D configuration. The samples are extruded to produce 3-D CAD model of sandwich shape porous structures. The different samples are tested with universal compression machine and mechanical characteristics of the models are investigated. Furthermore, the energy absorption efficiency and load bearing capability of samples are studied. The results of the experimental procedure are compared to numerical simulations under quasi-static condition.
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    Mechanical properties and energy absorbing capabilities of Z-pinned aluminum foam sandwich
    (Elsevier, 2019-04) Raeisi, Sajjad; Kadkhodapour, Javad; Tovar, Andres; Mechanical and Energy Engineering, School of Engineering and Technology
    Aluminum foam sandwich (AFS) structures are suitable for impact protection in lightweight structural components due to their specific energy absorption capability under compression. However, tailoring the deformation patterns of the foam cells is a difficult task due to the randomness of their internal architecture. The objective of this study is to analyze the effect of embedding aluminum pins into an AFS panel (Z-pinning) to better control its deformation pattern and improve its energy absorption capability. This study considers a closed-cell AFS panel and analyzes the effect of multi-pin layout parallel to the direction of the uniaxial compressive loading. The results of the experimental tests on the reference (without Z-pinning) AFS are utilized to develop numerical models for the reference and Z-pinned AFS structures. Physical experiments and numerical simulations are carried out to demonstrate the advantages of Z-pinning with aluminum pins. The results exhibit a significant increase in elastic modulus, plateau stress and energy absorption capability of the Z-pinned samples. Also, the effect of the pin size and Z-pinning layout on the mechanical performance of the Z-pinned AFS is also investigated using numerical simulations.